Patients with ALL in first or second remission will comprise the major patient group treated in randomized phase III trials proposed in this subproject. Based on promising results from the Memorial Sloan Kettering Transplant Team a comparison will be made between a schedule of 14.4 Gy of hyperfractionated TBI followed by CY and a fractionated TBI schedule of 15.75 Gy either preceded or followed by CY. Choice of the latter regimen will be determined by the results of an ongoing randomized trial comparing the administration of CY before or after TBI. Future Phase III trials will be designed using new treatment regimens developed in subprojects I.A. and I.B. We will identify risk factors associated with success or failure of marrow transplantation to define the role of marrow grafting in patients with ALL, especially those in first remission.